Comment 1 for bug 183585

I have found the culprit: /etc/resolvconf/update.d/libc, the script that takes the information from resolvconf and actually updates /etc/resolv.conf, is limited to three name servers. It takes information from the files in /etc/resolvconf/run/interface/, reading them in order as they are returned by /lib/resolvconf/list-records. This order is configured in /etc/resolvconf/interface-order. NetworkManager uses /etc/resolvconf/run/interface/NetworkManager, which has a surprisingly low priority -- it is caught by the "*" at the end of interface-order.

The fix, without removing resolvconf, is to add "NetworkManager" on a new line to /etc/resolvconf/interface-order right after the comment. resolvconf and its scripts will now take NetworkManager's opinion much more seriously than all the others'.